1. Field of the Invention
The present invention relates to an optical unit in which an optical member such as a pickup lens and a holding member are fixed to each other by laser welding by using laser light and to a method for fixing the optical member.
2. Description of the Related Art
The following methods for fixing an optical member such as a lens are hitherto known.
(1) After inserting a lens in a lens-holding member composed of a resin, the lens is fixed to the peripheral front edge of the lens-holding member by known thermal caulking or the like; and
(2) The external periphery of a lens and a lens-holding member are fixed to each other with a UV cure adhesive or the like.
Unfortunately, according to the method (1), a caulking tool melts the peripheral front edge of the lens-holding member by heat so as to cover the peripheral front edge of the lens, thereby leading to a longer time for caulking and an increase in assembling steps, accordingly resulting in an increased cost. Also, since the external periphery of the lens-holding member must be melted by heat with the caulking tool so as to have the peripheral front edge of the lens fixed thereto, the lens-holding member and the lens are inevitable subjected to a pressing force, thereby causing a guarantee problem of the positioning accuracy of the lens after assembly.
Also, according to the method (2), in a time period after application of a UV cure adhesive to irradiation of a ultra-violet ray, the liquid adhesive is flown out onto the peripheral surface of the lens-holding member, and when the flown-out adhesive is solidified with ultra-violet radiation, the solidified adhesive interferes with components around the solidified adhesive after assembly, thereby causing poor operation, especially deteriorating optical performance. Also, the liquid adhesive flows inside the lens through a gap between the lens-holding member and the external periphery of the lens, thereby causing a guarantee problem of the optical performance of the lens, or the like.
In order to solve these problems, Japanese Patent Laid-Open No. 2003-123512 discloses a method in which two resins are fixed to each other by laser welding. More particularly, a lens unit is made up by an outer lens composed of a transparent thermoplastic resin and a housing composed of a thermoplastic resin absorbent to laser light, and the housing and the outer lens are welded with each other by emitting laser light from a side wall of the outer lens in a state in which the external periphery of the housing and the side wall are abutted against each other.
Also, methods for fixing an optical member such as a plastic lens to a lens frame or the like composed of a plastic by using laser light are disclosed. For example, Japanese Patent Laid-Open No. 2004-20867 discloses a method for fixing a plastic lens to, for example, a plastic lens-frame or a plastic finder frame by irradiating the lens-frame or the finder-frame with laser light.
In addition, Japanese Patent Laid-Open No. 2003-123506 discloses a method in which an outer lens composed of a transparent thermoplastic resin and a housing composed of another thermoplastic resin absorbent to laser light are welded with each other by irradiating the entire periphery of an inner sheet composed of a transparent thermoplastic resin with laser light from the outer lens side in a state in which the inner sheet is sandwiched at the abutment portion between the outer lens and the housing.